The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.
(1) Field of the Invention
The present invention relates generally to determining a camera""s optimal fstop, and more particularly to a method and apparatus for computing the fstop that provides optimal resolution for a specified depth-of-field.
(2) Description of the Prior Art
It is well known that a camera""s fstop controls the depth-of-field in a photographic image. The depth-of-field is the region in which objects remain focused, and objects outside the depth-of-field are not focused. For a given depth-of-field, another measure of image quality is the resolution, or image sharpness, within that depth-of-field. The depth-of-field resolution is determined by film properties (grain size), lens properties (focal length and aperture), light properties (wavelength), and depth-of-field size.
Because depth-of-field and resolution are each affected by a camera""s fstop, photographers often compromise depth-of-field for increased resolution, or vice-versa. U.S. Pat. No. 4,785,323 details a method of selecting an aperture/shutter combination with an optimum depth-of-field to blur ratio, but maximum resolution throughout the depth-of-field is not considered. Alternately, U.S. Pat. No. 4,792,823 describes a manual depth-of-field preview device in which an optimum depth-of-field is user-determined by previewing images. Again, optimum settings are not computed or considered. U.S. Pat. Nos. 5,049,916 and 5,130,739 optimize photographic exposure through extra system speed, but sacrifice depth-of-field for shutter speed to minimize blur from system and object motion. These patents do not address picture sharpness or depth-of-field control. U.S. Pat. No. 5,532,782 provides calculations for an fstop that ensure focus for multiple objects at various distances; however, maximum sharpness or resolution is not addressed.
There is currently no method or apparatus for computing the maximum resolution or image sharpness within a predefined depth-of-field. What is needed is a method and apparatus that allow a photographer to compute fstop for optimal resolution throughout a predetermined depth-of-field.
It is a general purpose and object of the present invention to provide a method and apparatus to compute fstop to provide maximum image resolution or sharpness.
It is a further object to provide such computation for a predetermined depth-of-field specified by the photographer.
It is yet another object to provide such computation in an exact manner, and in an approximate manner for relative computational ease.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
These objects are accomplished with the present invention by a method and apparatus to determine fstop that provides optimal image resolution for a predetermined depth-of-field. An approximate and exact method and apparatus are provided to determine the optimal resolution fstop. The optimal resolution fstop is a function of the lens focal length, depth-of-field in front of the object, wavelength of light, and distance of the object to the lens center. Once the optimal resolution fstop is determined, the camera is adjusted to the closest discrete fstop available. When the approximate field technique is utilized, the camera must be adjusted to the discrete fstop closest to, but not exceeding, the computed fstop.